Impact absorber device

ABSTRACT

An impact absorber device includes at least one first portion having a short tubular shape, and at least one second portion having a short tubular shape concentrically disposed in a stacked relationship with the first portion. The first portion and the second portion engage with each other at an engagement portion which is inclined with respect to a concentric axis of the first portion and the second portion. With this arrangement, impact energy is absorbed in the case of collision accidents of vehicles such as an automobile and trains, and the dropping accidents of lifts such as elevators.

This is a Divisional of U.S. application Ser. No. 11/661,036, filed onFeb. 26, 2007, and allowed on Feb. 18, 2011, the subject matter of whichis incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a device for absorbing impact energy inthe case of a collision accident of vehicles such as automobiles andtrains, and drop accidents of lifts such as elevators.

BACKGROUND ART

An impact absorber device sometimes referred to as a “crash box” isinstalled on a front part of a chassis frame of a vehicle in order toabsorb energy of a collision crush impact. The impact absorber deviceabsorbs the impact energy by way of buckling deformation when a load ofthe impact applied thereto exceeds a predetermined level. Installationof this device thus ensures the safety of individuals in the vehicle.

In Japanese Patent Kokai No. 2002-39245, for example, such an impactabsorber device made of aluminum alloy casting is disclosed.

This impact absorber device has a cylinder portion made of aluminumalloy casting, and the wall thickness of the tubular portioncontinuously or partially changes along an axial direction. With thisconfiguration, the impact energy is effectively absorbed by performingplastic deformation in longitudinally alternating inward and outwardcorrugations along the axial direction of the tubular portion.

Japanese Patent Kokai No. 2004-100557 discloses another impact absorberdevice of which entire body is made of metal. This impact absorberdevice includes a tubular portion, flanges respectively provided on bothsides of the tubular portion, and a reinforcing member formed around thetubular portion. The wall thickness of the tubular portion partially orentirely varies gradually from one side to the other.

There are other impact absorber devices which rely upon crack extensionor deformation of a honeycomb element for absorbing the impact energy.An impact absorber device of crack extension type absorbs the impactenergy by extending a crack which is triggered when a tapered member ispressed onto an end portion of the cylindrical element. An impactabsorber device of a honeycomb element deformation type absorbs theimpact energy by buckling and crashing a side wall of a honeycomb panelinstalled between flat plates.

Since the above mentioned conventional impact absorber devices rely onsuch unstable phenomena as buckling deformation and cracking extension,deformation mode (or deforming pattern) considerably changes even byslight difference in dimension, installation condition or constraintcondition, which may occur during manufacturing and installation phases.Further, deformation mode is greatly influenced by the impact directionof the load at collision.

An impact absorber device of buckling type requires a longer body toabsorb greater impact energy in the axial direction. This raises aconcern that the longer body may cause Euler buckling during absorptionof the impact energy. As a result, an absorbing element with the longerbody may fail to function properly. Moreover, during the bucklingdeformation, the impact energy is absorbed by longitudinally alternatinginward and outward corrugations as mentioned above, which generatesoscillation in a load-to-length-change response. Accordingly, the entireelement cannot be effectively used to absorb the impact energy.

An impact absorber device of crack extension type may vary its crackextension pattern depending on a trigger condition for the cracking suchas a contact angle between the impact absorber device and a member totrigger crack in the device. Therefore, it may be very difficult tocontrol the extension of the crack. An impact absorber device of ahoneycomb element deformation type inherently has a complicatedstructure, and therefore it is very difficult to fabricate the device asexpected and properly evaluate the performance of the device.

DISCLOSURE OF THE INVENTION

In consideration of the foregoing problems, it is an object of thepresent invention to provide an impact absorber device installed in alimited space so as to efficiently absorb impact energy in a stablemanner.

An impact absorber device according to the present invention includes atleast one first portion having a short tubular shape, and at least onesecond portion having a short tubular shape concentrically disposed in astacked relationship with the first portion. The first portion and thesecond portion engage with each other at an engagement portion which isinclined with respect to a concentric axis of the first portion and thesecond portion.

The impact absorber device according to the present invention may beprovided with the first portion having a small diameter and having afull peripheral sliding contact face at a top portion thereof, thesecond portion having a large diameter and having a full peripheralsliding contact face at a bottom portion thereof, the engagement portionof a truncated cone connecting the first portion and the second portionso that the full peripheral sliding contact faces are directed inopposite directions. The first portion, the second portion and theconnection portion may constitute one unit. The impact absorber devicemay further include support elements for supporting one or a pluralityof the unit(s) from both sides. The support element may have a slidingcontact surface on a side facing the unit.

Each of the first portion and the second portion of the impact absorberdevice according to the present invention may have a short cylindricalshape. Radiuses of the cylindrical shapes of the first portion and thesecond portion respectively measured on the basis of the center of wallthickness thereof may be different from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a first embodiment of an impactabsorber device 10 according to the present invention;

FIG. 2 is a partial cross-sectional view showing a modification of thefirst embodiment of the impact absorber device 10 according to thepresent invention;

FIG. 3 is a diagram showing action and reaction forces applied to theimpact absorber device 10 of FIG. 1;

FIG. 4 shows diagrams illustrating how the impact absorber device 10 ofFIG. 1 deforms while absorbing impact energy;

FIG. 5 is a schematic partial cross-sectional view showing the impactabsorber device 10 of FIG. 1 installed on a front part of a chassisframe of an automobile;

FIG. 6 shows cross-sectional views of modifications of the firstembodiment using a plurality of the impact absorber devices 10 accordingto the present invention;

FIG. 7 shows partial cross-sectional views of the first embodiment ofthe impact absorber device 10 which is provided with an engagingsection;

FIG. 8 is a diagram showing a relationship of the load and length-changeof the impact absorber device 10 of FIG. 1;

FIG. 9 is a cross-sectional view showing a second embodiment of animpact absorber device 20 according to the present invention;

FIG. 10 are diagrams showing action and reaction forces applied to ashock absorbing element 30 of the impact absorber device 20 of FIG. 9,and illustrating how the shock absorbing element 30 deforms whileabsorbing impact energy;

FIG. 11 shows cross-sectional views illustrating a modification of thesecond embodiment of the impact absorber device 20 in which a pluralityof shock absorbing elements 30 are used;

FIG. 12 is a diagram showing a relationship of the load andlength-change of the shock absorbing element 30 of the impact absorberdevice 20 of FIG. 9;

FIG. 13 is a cross-sectional view showing a third embodiment of animpact absorber device 300 according to the present invention;

FIG. 14 shows partial cross-sectional views illustrating modificationsof a connection portion of the third embodiment of the presentinvention;

FIG. 15 shows partial cross-sectional views illustrating how the impactabsorber device 300 of FIG. 13 deforms while absorbing impact energy;

FIG. 16 shows cross-sectional views illustrating modifications of thethird embodiment in which a plurality of the units 310 are used;

FIG. 17 is a cross-sectional view showing a fourth embodiment of animpact absorber device 400 according to the present invention;

FIG. 18 shows partial cross-sectional views illustrating how the impactabsorber device 400 of FIG. 17 deforms while absorbing impact energy;

FIG. 19 shows cross-sectional views illustrating modifications of thefourth embodiment in which a plurality of the units 410 are used; and

FIG. 20 is a table comparing the energy absorption efficiencies ofvarious impact absorber devices.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be hereinafter described withreference to the drawings.

FIG. 1 is a cross-sectional view of a first embodiment of an impactabsorber device 10 according to the present invention.

The impact absorber device 10 includes a first element 11 having a shorttubular shape and a second element 12 having a short tubular shape. Thefirst element 11 and the second element 12 are concentrically stackedone on another when in use. When an impact load Fi is applied to theimpact absorber device 10, the first element 11 is pressed and insertedinto the second element 12. Accordingly, the first element 11 deforms toshrink in a radially inward direction, thereby decreasing its diameter.Simultaneously, the second element 12 deforms to expand in a radiallyoutward direction, thereby increasing its diameter. As a result theimpact energy is absorbed. The impact absorber device 10 is generallyinstalled between rigid members such as rigid plates 13 and 14 as shownin FIG. 1.

The first element 11 may be made of metal such as stainless, aluminumalloy and magnesium alloy, or nonmetal such as ceramic, plastic, and soforth. The first element 11 has an inclined face 11 a at the bottomportion facing the second element 12 so as to engage with the secondelement 12 when the first element 11 and the second element 12 aredisposed in a stacked relationship. The first element 11 may haveanother inclined face 11 a at the top portion of the first element 11,and in this case, two second elements 12 may be respectively stacked ontop and bottom of the first element 11. The second element 12 has aninclined face 12 a at the top portion thereof facing the first element11 so as to engage with the first element 11 when the second element 12and the first element 11 are disposed in a stacked relationship. Thesecond element 12 may have another inclined face 12 a at the bottomportion of the second element 12, and in this case, two first elements11 may be respectively stacked on top and bottom of the second element12. The second element 12 may be made of metal such as stainless,aluminum alloy and magnesium alloy, or nonmetal such as ceramic,plastic, and so forth. It is to be noted that the material of the secondelement 12 is not necessarily the same as that of the first element 11.Difference in material between the first element 11 and the secondelement 12 makes it possible to control the deformation where, forexample, only one of the elements may be deformed when absorbing aspecified impact energy.

The inclination angle of the inclined face 11 a of the first element 11with respect to a plane perpendicular to the central axis is the same asthe inclination angle of the inclined face 12 a of the second element 12with respect to a plane perpendicular to the central axis, which is anangle of θ₁. The angle θ₁ is preferably within a range of 30° to 85°,and most preferably about 60°.

The second element 12 may also have an additional inclined face atradially inside or outside of the inclined face 12 a. An inclinationangle of the additional inclined face with respect to a planeperpendicular to the central axis is different from the inclinationangle of the inclined face 12 a. With this arrangement, it may bepossible to control an extent of the deformation and to stabilize thedeformation during the expansion and shrink of the elements in a radialdirection. FIG. 2 shows an example of such an additional inclined face12 b having an inclination angle of θ₁′ that is formed radially insideof the inclined face 12 a.

The impact absorber device 10 has, for example, the followingdimensions: an outer diameter, inner diameter and height of the cylinderof the first element 11 are 40 mm, 32 mm and 12.4 mm, respectively, andan outer diameter, inner diameter and height of the cylinder of thesecond element 12 are 40 mm, 32 mm and 12.3 mm, respectively. The impactabsorber device 10 may have other dimensions on condition that theheight of the element is shorter than the buckling wavelength (λ)thereof so as to prevent local buckling (corrugation) and Eulerbuckling. The most preferable shape of the impact absorber device 10 hassuch a feature that that the diameter of each element measured based onthe center of the wall thickness is greater than the height thereof. Itshould be noted that the above-described buckling wavelength (λ) dependson the shape of the cylinder, and is generally defined as a function ofthe wall thickness ratio t/R, where t is a wall thickness of thecylinder, and R is a radius of the cylinder measured based on the centerof the wall thickness.

With this arrangement, it can be expected that the first element 11 andthe second element 12 uniformly deform during the expansion and shrinkin a radial direction without causing buckling deformation. In thefollowing description, the above described shape having the feature ofthe height being shorter than the buckling wavelength thereof will bereferred to as a “short tubular shape”, and in particular the abovedescribed shape having a cylindrical form will be referred to as a“short cylindrical shape”.

The forms of the first element 11 and the second element 12 are notlimited to the short cylindrical shapes of which each cross-section is acircle as shown in FIG. 1. Alternatively, the first element 11 and thesecond element 12 may have short tubular shapes of which eachcross-section is an ellipse or polygon.

As shown in FIG. 3, when the impact absorber device 10 having theconfiguration of the first embodiment of the present invention receivesan impact load Fi in a direction of the central axis C thereof, a forceFa is applied to the second element 12 in a direction perpendicular tothe inclined face 12 a. Simultaneously, a force Fr is applied to thefirst element 11 in a direction perpendicular to the inclined face 11 aas a reaction force of the force Fa. Consequently, an outward force Fewhich is a horizontal component of force Fa (outward component of forceFa which is perpendicular to the central axis C) is applied to thesecond element 12, thereby expanding the second element 12 in a radiallyoutward direction. When the force Fe applied to the second element 12exceeds a predetermined threshold, the second element 12 causes plasticdeformation after increasing its diameter, thereby absorbing the impactenergy. On the other hand, an inward force Fc which is a horizontalcomponent of the force Fr (inward component of the force Fr which isperpendicular to the central axis C) is applied to the first element 11,thereby shrinking the first element 11 in a radially inward direction.When a force Fc applied to the first element 11 exceeds a predeterminedthreshold, the first element 11 causes plastic deformation afterdecreasing its diameter, thereby absorbing the impact energy. Thedeformation of the first element 11 and the second element 12 is notbuckling deformation but is expansion and shrink in a radial directionof the entire first element 11 and second element 12. FIG. 4A to FIG. 4Eshow a progress of this deformation. FIG. 4A is a state before theimpact load is applied to the impact absorber device 10. FIG. 4B to FIG.4E show the progress of deformation, and FIG. 4E shows the state whenthe deformation is completed. As shown in FIG. 4B to FIG. 4E, as thefirst element 11 is pressed into the hollow portion inside the secondelement 12, an upper part of the second element 12 is deformed to expandin a radially outward direction.

FIG. 5 shows an example when the impact absorber device 10 of the firstembodiment is installed in an automobile 50. Here 51 indicates a frontpart of a chassis frame, and 52 indicates a bumper. The impact absorberdevice 10 is installed between the front part of the chassis frame 51and the bumper 52, and an impact energy received by the bumper 52 atcollision is absorbed by the impact absorber device 10.

The impact absorber device 10 has been described on the basis of a pairof the first element 11 and the second element 12 with reference to FIG.1, but the present invention is not limited to this configuration. Theimpact absorber device 10 may include a plurality of first elements andsecond elements. For example, the impact absorber device 10 may includetwo first elements 11 and one second element 12 as shown in FIG. 6A, onefirst element 11 and two second elements 12 as shown in FIG. 6B, or twofirst elements 11 and two second elements 12 as shown in FIG. 6C, whichare stacked one on another.

In FIG. 6A to FIG. 6C, two first elements 11 are the same to each other,and two second elements 12 are the same to each other. Alternatively, asshown in FIG. 6D, a first element 11 positioned near a plate 13 may havedifferent shape or material from another first element 11′ positionedfar from the plate 13. In a similar manner, a second element 12positioned near a plate 13 may have different shape or material fromanother second element 12′ positioned far from the plate 13. Thisarrangement makes it possible for two pairs of elements of 11, 12 and11′, 12′ to share different types of the impact. For example, energyfrom a weak crush impact is absorbed by one pair of elements of 11 and12 positioned near the plate 13 and energy from a strong crush impact isabsorbed by the other pair of elements 11′ and 12′ positioned far fromthe plate 13. Accordingly, installation of a plurality of pairs ofdevices with different shapes or materials in a vehicle ensures safetyof individuals on board from collision at low speed to collision at highspeed. Further, as shown in FIG. 6E, a plurality of sets of stackedfirst and second elements may be arranged horizontally. This arrangementmakes it possible to disperse the impact load in absorbing the impactenergy.

The impact absorber device 10 may be provided with fixing means so asnot to cause a misalignment of the elements 11 and 12 which may becaused by unanticipated situations such as vibration after installationor impact in a diagonal direction. Such fixing means may be, forexample, a cylindrical housing that encloses whole impact absorberdevice, or two panels for sandwiching the entire impact absorber devicetherebetween with a shaft passing through the central axis of theelements 11 and 12 for securing the panels to the device. The elements11 and 12 may be glued to each other by adhesive, welding, soldering orthe like to an extent where the functions of the impact absorber deviceare not interfered with. Further, the impact absorber device 10 may beprovided with an engaging portion at the outermost circumference sectionor innermost circumference section so as to easily stack the elements 11and 12 one on another. FIG. 7A and FIG. 7B show examples of suchengagement sections 11 c and 11 d. FIG. 7A shows an engagement section11 c which is formed at the outermost circumference section of the firstelement 11. The engagement section 11 c has an all around horizontalface of which width is about 1 to several mm on a side facing the secondelement 12. The first element 11 thus engages with the second element 12by this all around horizontal face. FIG. 7B, on the other hand, shows anengagement section 11 d, which is formed at the innermost circumferencesection of the first element 11. The engagement section 11 d has an allaround fitting portion of which width is about 1 to several mm on a sidefacing the second element 12. The all around fitting portion thus fitsinto the second element 12, and therefore the first element 11 engageswith the second element 12. It should be noted that, in FIG. 7A, theinner and outer diameters of the first element 11 are the same as thoseof the second element 12, but in FIG. 7B, the inner diameter of thefirst element 11 is smaller than that of the second element 12, and theouter diameter of the first element 11 is smaller than that of thesecond element 12.

FIG. 8 is a diagram showing the relationship of the load andlength-change when the impact absorber device 10 of the first embodimentreceived an impact load and deformed, where the impact absorber device10 of the first embodiment of the present invention is compared with aconventional impact absorber device. The abscissa in FIG. 8 shows alength-change of the impact absorber device which is a displacement of acontact point between the rigid body and the impact absorber device. Thecontact point was displaced due to deformation of the impact absorberdevice placed on a load cell as a result of a strike by the rigid bodydropped thereon with a velocity of 40 km/hr. The ordinate in FIG. 8shows a value indicated by the load cell at each location of thedisplacement.

The device of the first embodiment of the present invention in FIG. 8had seven first elements 11 and eight second elements 12, which werewholly made of aluminum alloy. The inclination angles of the inclinedfaces were all 60°. The conventional device, on the other hand, had acylinder shape made of aluminum alloy, of which wall thickness was 4 mmand the radius was 30 mm.

As FIG. 8 shows, the conventional impact absorber device had anoscillating load-to-length-change response after the initial peak loadin absorbing the impact energy. In addition, each loop in the wave ofthe oscillating response had a finer waveform. The impact absorberdevice of the first embodiment, on the other hand, had an approximatelyuniform load-to-length-change response in absorbing the impact energy.

As described above, the impact absorber device 10 of the firstembodiment of the present invention can absorb the impact energy in muchmore stable manner without generating unfavorable conditions such as aninitial peak load, oscillation of the response, and fine waveform ineach loop in the wave of the oscillation, which are generated in theconventional impact absorber device during the impact absorption. Thisis because the present invention primarily uses expansion and shrinkphenomena in a radial direction which generates uniform deformation,without using the buckling phenomena which causes sudden deformationwhen a load exceeds a threshold level. Further, the deformation mode ofthe impact absorber device 10 of the first embodiment of the presentinvention is mainly attributed to the expansion and shrink of theelements in a radial direction, so that deformation mode is more stableas compared with the buckling phenomenon which inherently has anunstable feature. Therefore it becomes possible to suppress change indeformation mode caused by slight deviation of dimension, installationcondition and constraint condition which may occur during manufacturingand installation phases. Moreover, since the impact absorber device 10of the first embodiment absorbs the impact energy by uniformly deformingthe entire elements, energy absorption efficiency, which is the totalamount of absorbed energy divided by unit weight of the impact absorberdevice 10, is higher than that of the conventional impact absorberdevice. FIG. 20 shows a table comparing the energy absorptionefficiencies of several impact absorber devices. The energy absorptionefficiency of the first embodiment of the present invention is 79.1KJ/kg, which is about six times as compared with a conventional impactabsorber device which uses buckling deformation. Further, since thestructure of the impact absorber device 10 is simple, designspecification of the device such as peak load and load-to-length-changerelationship can be easily evaluated, and the impact absorber device 10can be easily manufactured with reduced cost.

The second embodiment of the present invention will be hereinafterdescribed.

FIG. 9 is a cross-sectional view of an impact absorber device 20according to the second embodiment of the present invention.

The impact absorber device 20 includes a shock absorbing element (unit)30 and support elements 40 which support the shock absorbing element 30from both sides. The shock absorbing element 30 has a small diameterportion 31 in a short tubular shape, a large diameter portion 32 in ashort tubular shape, and an intermediate portion 33 in a truncated coneshape for connecting these portions 31 and 32 concentrically. The smalldiameter portion 31, large diameter portion 32 and intermediate portion33 are integrated into one piece. When the impact load Fi is applied tothe shock absorbing element 30, the small diameter portion 31 is pushedinto the large diameter portion 32 and is deformed to shrink in a radialdirection. Simultaneously, the large diameter portion 32 is deformed toexpand in a radial direction. Accordingly, the impact energy isabsorbed. The impact absorber device 20 is made of metal such asstainless, aluminum alloy and magnesium alloy, or nonmetal such asceramic, plastic, and so forth. Materials of these elements are notnecessarily the same with respect to each other. The small diameterportion 31 has a full peripheral sliding contact face 31 a at the topend, and the large diameter portion 32 has a full peripheral slidingcontact face 32 a at the bottom end. A top end of the truncated coneshape of the intermediate portion 33 is connected to the small diameterportion 31, and the bottom end thereof is connected to the largediameter portion 32, so that the full peripheral sliding contact faces31 a and 32 a of the small diameter portion 31 and the large diameterportion 32 respectively face the opposite direction from each other. Thesupport element 40 includes a top side support element 40-1 and a bottomside support element 40-2, both having the plate shapes. The top sidesupport element 40-1 has a sliding face 40-1 a on a surface facing theshock absorbing element 30 so as to slidably contact with the smalldiameter portion 31. The bottom side support element 40-2, on the otherhand, has a sliding face 40-2 a on a surface facing the shock absorbingelement 30 so as to slidably contact with the large diameter portion 32.

The inclination angle between the side face of the truncated cone andthe sliding face of the bottom side support element is defined as θ₂,and this inclination angle θ₂ is preferably within a range of 5° to 60°,and most preferably about 30°.

The shock absorbing element 30 has, for example, the followingdimension: an outer diameter, inner diameter and the height of thecylinder of the small diameter portion 31 are 28 mm, 20 mm and 6 mm,respectively, and an outer diameter, inner diameter and the height ofthe cylinder of the large diameter portion 32 is 56 mm, 48 mm and 6 mm,respectively. An overall height of the shock absorbing element 30 withthe intermediate portion 33 connecting these portions is 15 mm. Theshock absorbing element 30 may have other dimensions on condition thatthe height of the small diameter portion 31 is shorter than the bucklingwavelength (λ) thereof and the height of the large diameter portion 32is shorter than the buckling wavelength (λ) thereof. With thisarrangement, it can be expected that the small diameter portion 31 andlarge diameter portion 32 uniformly deform during expansion or shrink ina radial direction without causing buckling deformation.

The forms of the small diameter portion 31 and large diameter portion 32are not limited to the short cylindrical shapes of which eachcross-section is a circle as shown in FIG. 9. Alternatively, the smalldiameter portion 31 and large diameter portion 32 may have short tubularshapes of which each cross-section is an ellipse or polygon.

With this configuration, when the impact absorber device 20 receives animpact load Fi in a direction of the central axis C thereof as shown inFIG. 10B, a force Fa is applied to the large diameter portion 32 fromthe intermediate portion 33. Simultaneously, the force Fr is applied tothe small diameter portion 31 from the intermediate portion 33 as areaction force of the force Fa. Consequently, an outward force Fe whichis a horizontal component of the force Fa (outward component of theforce Fa which is perpendicular to the central axis C) is applied to thelarge diameter portion 32, thereby expanding the large diameter portion32 in a radially outward direction while the full peripheral slidingface 32 a thereof slides on the sliding face 40-2 a of the bottom sidesupport element 40-2. When the force Fe applied to the large diameterportion 32 exceeds a predetermined threshold, the large diameter portion32 causes plastic deformation after increasing its diameter, therebyabsorbing the impact energy. On the other hand, an inward force Fc whichis a horizontal component of the force Fr (inward component of the forceFr which is perpendicular to the central axis C) is applied to the smalldiameter portion 31, thereby shrinking the small diameter portion 31 ina radially inward direction while the full peripheral sliding face 31 aslides on the sliding face 40-1 a of the top side support element 40-1.When the force Fc applied to the small diameter portion 31 exceeds apredetermined threshold, the small diameter portion 31 causes plasticdeformation after decreasing its diameter, thereby absorbing the impactenergy. The deformation of the small diameter portion 31 and largediameter portion 32 is not buckling deformation but is deformation bycompression and expansion/shrink in a radial direction of the entiresmall diameter portion 31 and large diameter portion 32, and by thefolding of the intermediate portion 33. FIG. 10A to FIG. 10D show aprogress of this deformation. FIG. 10A is a state before the impact loadis applied to the impact absorber device 20. FIG. 10B to FIG. 10D showthe progress of the deformation, and FIG. 10D shows the state when thedeformation is completed. AS shown in FIG. 10A to FIG. 10D, asdeformation progresses, the heights of the small diameter portion 31 andlarge diameter portion 32 decreases due to compression, and the wallthicknesses of the small diameter portion 31 and large diameter portion32 increase. As readily understood from FIG. 10D, when the deformationcompletes, the small diameter portion 31 is inserted into a hollowportion radially inside the large diameter portion 32, so that theentire shock absorbing element 30 becomes substantially flat.

The impact absorber device 20 has been described on the basis of oneshock absorbing element 30 supported by the support element 40, but thepresent invention is not limited to this configuration. The impactabsorber device 20 may include two or more shock absorbing elements 30which are vertically stacked one on another as shown in FIGS. 11A, 11B,11C and 11D. When a plurality of shock absorbing elements are used, theshock absorbing elements may have different shapes and materials asshown in FIG. 11E. This arrangement makes it possible for the differentshock absorbing elements to share different type of the impact. Forexample, energy from a weak crush impact is absorbed by one shockabsorbing element 30 positioned near a supporting element 40-1 andenergy from a strong crush impact is absorbed by the other shockabsorbing element 30′ positioned far from the supporting element 40-1.Accordingly, installation of a plurality of shock absorbing elementswith different shapes or materials in a vehicle ensures safety ofindividuals on board from collision at low speed to collision at highspeed. Further, even though a plurality of the shock absorbing elements30 are arranged such that a small diameter portion 31 of one elementfaces a small diameter portion 31 of the other, and a large diameterportions 32 of one element faces a large diameter portions 32 of theother as in FIGS. 11A to 11F, the shock absorbing elements 30 may bearranged in a different manner. Specifically, as shown in FIG. 11F, aplurality of shock absorbing elements 30 may be stacked one on anothersuch that the small diameter portion 31 faces the large diameter portion32 via a sliding element 45 with sliding faces on both sides. In otherwords, a plurality of shock absorbing elements 30 may be stacked in thesame direction. Moreover, a plurality of shock absorbing elements 30 maybe arranged horizontally as shown in FIG. 11G. This arrangement makes itpossible to disperse the impact load in absorbing the impact energy.

The impact absorber device 20 may by provided with fixing means so asnot to cause a misalignment of the elements which may be caused byunanticipated situations such as vibration after installation or byimpact in a diagonal direction. Such fixing means may be, for example, acylindrical housing that encloses whole impact absorber device, or ashaft for securing the support element 40 by passing through the centralaxis of the elements. The elements may be glued to each other byadhesive, welding, soldering or the like to an extent where thefunctions of the impact absorber device are not interfered with.

FIG. 12 is a diagram showing the relationship of the load andlength-change when the impact absorber device 20 of the secondembodiment of the present invention received an impact load anddeformed, where the impact absorber device 20 of the second embodimentof the present invention is compared with a conventional impact absorberdevice. The relationship of the abscissa and ordinate in FIG. 12 issimilar to that in FIG. 8.

The device of the present invention in FIG. 12 had eight elements 30,which were arranged such that small diameter portions 31 were faced toeach other and large diameter portions 32 were faced to each other.Materials of the devices were wholly aluminum alloy. The conventionaldevice, on the other hand, had a cylinder shape made of aluminum alloy,of which wall thickness was 2 mm and the radius was 40 mm.

As FIG. 12 shows, the conventional impact absorber device had anoscillating load-to-length-change response after the initial peak loadin absorbing the impact energy. In addition, each loop in the wave ofthe oscillating response had a finer waveform. The impact absorberdevice of the second embodiment, on the other hand, had an approximatelyuniform load-to-length-change response in absorbing the impact energy.

As described above, the impact absorber device 20 of the secondembodiment of the present invention can absorb the impact energy in muchmore stable manner without generating unfavorable conditions such as aninitial peak load, oscillating of the load, and fine waveform in eachloop in the wave of the oscillating load, which are generated in theconventional impact absorber device during the impact absorption. Thisis because the present invention primarily uses expansion and shrinkphenomena in a radial direction which generates uniform deformation,without using the buckling phenomena which causes sudden deformationwhen a load exceeds a threshold level. Further, the deformation mode ofthe impact absorber device 20 of the second embodiment of the presentinvention is mainly attributed to the expansion and shrink of the largediameter portion and small diameter portion in a radial direction, andto the folding of the intermediate portion, so that deformation mode ismore stable as compared with the buckling phenomena which inherently hasan unstable feature. Therefore it becomes possible to suppress change indeformation mode caused by slight deviation of dimension, installationcondition and constraint condition which may occur during manufacturingand installation phases. Moreover, since the impact absorber device 20of the second embodiment absorbs the impact energy by uniformlydeforming the entire small diameter portion and large diameter portion,energy absorption efficiency, which is the total amount of absorbedenergy divided by unit weight of the impact absorber device 20, ishigher than that of the conventional impact absorber device. Further,since the structure of the impact absorber device 20 is simple, designspecification of the device such as peak load, load-to-length-changerelationship and other design values can be easily evaluated, and theimpact absorber device 20 can be easily manufactured with reduced cost.Furthermore, since the impact absorber device of the second embodimentis integrally formed as one unit, it becomes possible to cover variousload displacements and to easily control various energy absorptions.Furthermore, since the impact absorber device of the second embodimenthas no relative sliding portion between the expanding element andshrinking element owing to the integrally formed structure, whichalthough is necessary for the impact absorber device of the firstembodiment, it becomes possible for the impact absorber device of thesecond embodiment to provide highly rigid property and resistanceproperty against bending, shearing, vibration, and so forth, and itmakes easier to install the device in a necessary location.

The third embodiment of the present invention will be hereinafterdescribed.

FIG. 13 is a cross-sectional view of a third embodiment of an impactabsorber device 300 according to the present invention.

The impact absorber device 300 of this embodiment includes a unit 310which is integrally formed from two first portions 301 each having ashort cylindrical shape 301, one second portion 302 having a shortcylindrical shape, and two connection portions 303. Specifically, onesecond portion 302 is concentrically disposed between two first portions301, and the connection portion 303 is provided between the firstportion 301 and the second portion 302. The inner diameter of the firstportion 301 is smaller than that of the second portion 302, and theouter diameter of the first portion 301 is smaller than that of thesecond portion 302. In other words, the radius r1 of the cylinder of thefirst portion 301 measured on the basis of the center of its wallthickness is smaller than the radius r2 of the cylinder of the secondportion 302 measured on the basis of the center of the wall thickness.In order to form this arrangement, the connection portion 303 has aninclined portion which is inclined with respect to the concentric axis Cof the unit 310. In embodiment of the unit 310 shown in FIG. 13, eachconnection portion 303 has two inclined portions 303 a and 303 c. Astraight portion 303 b is provided between these two inclined portions303 a and 303 c, but this straight portion 303 b can be omitted. FIG.14A to FIG. 14D are partial cross-sectional views showing modificationsof the connection portion 303 having no straight portion 303 b. Theinclination angles of the inclined portions 303 a and 303 c with respectto the concentric axis C are θ₁ and θ₂ respectively, and these anglesare both 45°, for example. It should be noted that these angles are notlimited to this value, but are determined to obtain optimum valuesconsidering design parameters such as design impact load, specifiedextent of energy absorption, size of the impact absorber device and itsmaterial. The angles θ₁ and θ₂ need not be the same value. The impactabsorber device 300 is generally installed between rigid members such asrigid plates 320 a and 320 b as shown in FIG. 13.

The unit 310 of the impact absorber device 300 may be made of metal suchas stainless, aluminum alloy and magnesium alloy, or nonmetal such asceramic, plastic, and so forth. The impact absorber device 300 has, forexample, the following dimensions: inner diameter, wall thickness andheight of the first portion 301 are 30 mm, 4 mm and 10 mm, respectively,and inner diameter, wall thickness and height of the second portion 302are 32 mm, 4 mm and 20 mm, respectively. The overall height of the unitis 50 mm. The impact absorber device 300 may have other dimensions oncondition that each height of the first portion 301 and second portion302 is shorter than the buckling wavelength (λ) thereof. With thisarrangement, the first portion 301 and second portion 302 are compressedin the axial direction while maintaining the symmetrical deformationwith respect to the central axis C without causing buckling deformation.

When the impact absorber device 300 receives an impact load in adirection of the central axis C thereof, a compressing force to compressthe first portion 301 in the axial direction and a shrinking force toshrink the first portion 301 in a radially inward direction are appliedto the first portion 301 by the connection portion having an inclinedportion. When a force applied to the second portion 302 exceeds apredetermined threshold, the first portion 301 causes plasticdeformation, thereby absorbing the impact energy. On the other hand, acompressing force to compress the second portion 302 in the axialdirection and an expanding force to expand the second portion 302 in aradially outward direction are applied to the second portion 302 by theconnection portion having the inclined portion. When a force applied tothe second portion 302 exceeds a predetermined threshold, the secondportion 302 causes plastic deformation, thereby absorbing the impactenergy.

The deformation of the first portion 301 and second portion 302 is notbuckling deformation, but is expansion and shrink in a radial direction.FIG. 15A to FIG. 15H show a progress of this deformation. FIG. 15A toFIG. 15H show only one side in the cross-sectional view of one unit. Ineach cross-sectional view, an original shape of the unit beforedeformation is shown by a dotted line so as to visualize an extent ofthe deformation. FIG. 15A is a state before the impact load is appliedto the impact absorber device 300. FIG. 15B to FIG. 15H show theprogress of deformation, and FIG. 15H shows the state when deformationis completed. As understood from FIG. 15A to FIG. 15H, as deformationprogresses, compression of the first portion 301 causes increase of thewall thickness and shrink of the first portion 301 in a radially inwarddirection. Simultaneously, compression of the second portion 302 causesincrease of the wall thickness and expand of the second portion 302 in aradially outward direction. In addition, as the deformation progresses,the connection portion 303 is folded. It should be noted that, in thefirst portion 301, the inner diameter becomes somewhat smaller asdeformation progresses, but the outer diameter hardly changes. In thiscase, the shearing stress in the radial direction at both end faces ofthe unit is substantially zero. Accordingly, appropriately designedshape of the unit 310 makes it possible to control the deformation modeat both end faces of the unit. In the case shown in FIG. 15, forexample, the change of outer diameter at both end faces of the unit issuppressed, so that the outer circumference portion at both ends of theimpact absorber device 300 can be secured to the rigid plates 320 bysecuring means such as adhesive, welding and soldering, whilesubstantially ensuring the impact absorption performance. Therefore whena plurality of units are used, as mentioned later, impact absorptionperformance is hardly interfered with, even if adjacent units arecompletely integrated to each other. This means that when one impactabsorber device is fabricated by connecting a plurality of units 310,the impact absorber device can be securely installed at an installationlocation by merely securing both ends to rigid bodies.

The impact absorber device 300 of the third embodiment has beendescribed on the basis of one unit 310, but the present invention is notlimited to this configuration. The impact absorber device 300 mayinclude two or more units 310 which are stacked one on another. In thiscase, the units are integrated by being connected with each other bywelding, for example. As mentioned above, the shearing stress in theradial direction can be substantially zero in both end faces of oneunit, and therefore even if a plurality of units are stacked one onanother, the deformation mode of each unit can be substantiallyequalized. FIG. 16A shows a modification where three units 310 arestacked vertically. These units may be formed to have different shapesand materials to each other. This arrangement makes it possible fordifferent units to share different type of the impact. For example, twounits may be stacked such that one unit serves weak impact energy andthe other unit serves strong impact energy. FIG. 16B shows amodification where a unit 310 with a thin wall thickness and a unit 310′with a thick wall thickness are stacked one on another. When this deviceis installed in a vehicle, the safety of individuals on board can bewidely guaranteed from collision at low speed to collision at highspeed. Further, a plurality of units 310 may be arranged horizontally.FIG. 16C shows a modification where two units 310 are installed side byside. This arrangement makes it possible to disperse the impact load inabsorbing the impact energy.

Accordingly, the impact absorber device 300 of the third embodiment ofthe present invention can absorb the impact energy in much more stablemanner without generating an initial peak load, major change in load andfine waveform in each loop in the oscillation of the load, which aregenerated in the conventional impact absorber device during the impactabsorption. This is because the present invention uses stabledeformation phenomena such as expansion and shrink in a radial directionand compression, which simply increases the load as deformationprogresses without using the buckling phenomena which causes suddendeformation when a load exceeds a threshold value. Further, deformationmode of the impact absorber device 300 of the third embodiment of thepresent invention is mainly attributed to the compression andexpansion/shrink of the first portion 301 and second portion 302, andfolding of each portion influenced by the connection portion 303, sothat the deformation mode is more stable as compared with the bucklingphenomena, which inherently has an unstable feature. Therefore itbecomes possible to suppress change in deformation mode caused by slightdeviation of dimension, installation condition and constraint conditionwhich may occur during manufacturing and installation phases. Moreover,since the impact absorber device 300 of the third embodiment of thepresent invention absorbs the impact energy by uniformly deforming theentire first portion 301, second portion 302, and connection portion303, and therefore energy absorption efficiency, that is the totalamount of absorbed energy divided by unit weight of the impact absorberdevice 300, is higher than that of the conventional impact absorberdevice. FIG. 20 shows a table comparing the energy absorption efficiencyof several impact absorber devices. The energy absorption efficiency ofthe third embodiment of the present invention achieves 62.1 KJ/kg, whichis about 4.8 times as compared with a conventional impact absorberdevice. Further, since the structure of the impact absorber device 300is simple, design features such as load peak and load-displacementrelationship can be easily estimated, and the impact absorber device 300can be easily manufactured with reduced cost. Moreover, since the impactabsorber device of the present embodiment is integrally formed into oneunit, the impact absorber device may cover various load displacementsand may easily control various energy absorptions. Furthermore, sincethe impact absorber device of the present embodiment has no relativesliding portion between the expanding element and shrinking elementowing to the integrally formed structure, which is necessary for theimpact absorber device of the first embodiment, it becomes possible forthe impact absorber device to provide highly rigid property andresistance property against bending, shearing, vibration, and so forth,and also it becomes easier for the impact absorber device to beinstalled at a necessary location. Further, as described above, theouter diameter of the first portion 301 hardly changes during thedeformation. Therefore the unit 310 can be securely fixed to adesignated installation location by merely fixing both ends thereof tothe rigid plates, thereby making it possible for the impact absorberdevice to achieve specified performance even though the impact absorberdevice is subject to vibration, or the impact absorber device receivesthe impact in a diagonal direction.

The fourth embodiment of the present invention will be hereinafterdescribed.

FIG. 17 is a cross-sectional view of a fourth embodiment of an impactabsorber device 400 according to the present invention.

The impact absorber device 400 of this embodiment includes a unit 410which is integrally formed from two first portions 401 each having ashort cylindrical shape, one second portion 402 having a shortcylindrical shape, and two connection portions 403. Specifically, onesecond portion 402 is concentrically disposed between two first portions401, and the connection portion 403 is provided between the firstportion 401 and second portion 402. The inner diameter of the firstportion 401 is the same as the inner diameter of the second portion 402,and the outer diameter of the first portion 401 is greater than theouter diameter of the second portion 402. The radius r1 of the cylinderof the first portion 401 measured on the basis of the center of its wallthickness is greater than the radius r2 of the cylinder of the secondportion 402 measured on the basis of the center of the wall thickness.In order to form this arrangement, an inner diameter of the connectionportion 403 is the same as the inner diameters of the first portion 401and second portion 402, and the outer wall of the connection portion 403is inclined at the inclination angle θ₁ with respect to the concentricaxis C of the unit 410. The inclination angle θ₁ is 45°, for example. Itshould be noted that the angle θ₁ is not limited to this value, but isdetermined to obtain an optimum value considering design parameters suchas design impact load, specified extent of energy absorption, size ofthe impact absorber device and its material. The impact absorber device400 is generally installed between rigid members such as rigid plates420 a and 420 b as shown in FIG. 17.

The unit 410 of the impact absorber device 400 may be made of metal suchas stainless, aluminum alloy and magnesium alloy, or nonmetal such asceramic, plastic, and so forth. The impact absorber device 400 has, forexample, the following dimensions: inner diameter, wall thickness andheight of the first portion 401 are 21.2 mm, 7 mm and 6.8 mm,respectively, and inner diameter, wall thickness and height of thesecond portion 402 are 21.2 mm, 4 mm and 40 mm, respectively. Theoverall height of the unit is 60 mm. the impact absorber device 400 mayhave other dimensions on condition that each height of the first portion401 and second portion 402 is shorter than the buckling wavelength (λ)thereof. With this arrangement, the first portion 401 and second portion402 are compressed in the axial direction while maintaining thesymmetrical deformation with respect to the central axis C withoutcausing buckling deformation.

When the impact absorber device 400 receives an impact load in a centralaxis C direction, a compressing force to compress the first portion 401in the axial direction and a shrinking force to shrink the first portion401 in a radially inward direction are applied to the first portion 401by the connection portion having an inclined portion. When a forceapplied to the first portion 401 exceeds a predetermined threshold, thefirst portion 401 causes plastic deformation, thereby absorbing theimpact energy. On the other hand, a compressing force to compress thesecond portion 402 in the axial direction and an expanding force toexpand the second portion 402 in a radially outward direction areapplied to the second portion 402 by a connection portion having theinclined portion. When a force applied to the second portion 402 exceedsa predetermined threshold, the second portion 402 causes plasticdeformation, thereby absorbing the impact energy.

The deformation of the first portion 401 and second portion 402 is notbuckling deformation, but is expansion and shrink in a radial direction.FIG. 18A to FIG. 18H show a progress of this deformation. FIG. 18A toFIG. 18H show only one side in the cross-sectional view of one unit. Ineach cross-sectional view, an original shape of the unit beforedeformation is shown by a dotted line so as to visualize an extent ofthe deformation. FIG. 18A is a state before the impact load is appliedto the impact absorber device 400. FIG. 18B to FIG. 18H show theprogress of the deformation, and FIG. 18H shows the state when thedeformation is completed. As understood from FIG. 18A to FIG. 18H, asdeformation progresses, compression of the first portion 401 causesincrease of the wall thickness and shrink of the first portion 401 in aradially inward direction. Simultaneously, compression of the secondportion 402 causes increase of the wall thickness and expand of thesecond portion 402 in a radially outward direction. In addition, as thedeformation progresses, the connection portion 403 is folded. It shouldbe noted that, in the first portion 401, the outer diameter becomessomewhat larger as deformation progresses, but the inner diameter hardlychanges. In this case, the shearing stress in the radial direction atboth end faces of the unit is substantially zero. Accordingly,appropriately designed shape of the unit 410 makes it possible tocontrol the deformation mode at both end faces of the unit. In the caseshown in FIG. 18, for example, the change of inner diameter at both endfaces of the unit is suppressed, so that the inner circumferenceportions at both ends of the impact absorber device 400 can be securedto the rigid plates 420 by securing means such as adhesive, welding andsoldering, while substantially ensuring the impact absorptionperformance. Therefore when a plurality of units are used, as mentionedlater, impact absorption performance is hardly interfered with even ifadjustment units are completely integrated to each other. This meansthat when one impact absorber device is fabricated by connecting aplurality of units 410 by welding, the impact absorber device can besecurely installed at an installation location by merely securing bothends to rigid bodies.

The impact absorber device 400 of the fourth embodiment has beendescribed on the basis of one unit 410, but the present invention is notlimited to this configuration. The impact absorber device 400 mayinclude two or more units 410 which are stacked one on another. In thiscase, the units are integrated by being connected with each other bywelding, for example. As mentioned above, the shearing stress in theradial direction can be substantially zero in both end faces of oneunit, and therefore even if a plurality of units are stacked one onanother, the deformation mode of each unit can be substantiallyequalized. FIG. 19A shows a modification where three units 410 arestacked vertically. These units may be formed to have different shapesand materials to each other. This arrangement makes it possible fordifferent units to share different types of the impact. For example, twounits may be stacked such that one unit serves weak impact energy andthe other unit serves strong impact energy. FIG. 19B shows amodification where a unit 410 with a thin wall thickness and a unit 410′with a thick wall thickness are stacked one on another. When this deviceis installed in a vehicle, the safety of individual on board can bewidely guaranteed from collision at low speed to collision at highspeed. Further, a plurality of units 410 may be arranged horizontally.FIG. 19C shows a modification where two units 410 are installed side byside. This arrangement makes it possible to disperse the impact load inabsorbing the impact energy.

Accordingly, the impact absorber device 400 of the fourth embodiment ofthe present invention can absorb the impact energy in much more stablemanner without generating an initial peak load, major change in load andfine waveform in each loop in the oscillation of the load, which aregenerated in the conventional impact absorber device during the impactabsorption. This is because the present invention uses stabledeformation phenomena such as expansion/shrink in a radial direction andcompression, which simply increases load as deformation progresses,without using the buckling phenomena which causes sudden deformationwhen a load exceeds a threshold value. Further, deformation mode of theimpact absorber device 400 of the fourth embodiment of the presentinvention is mainly attributed to the compression and expansion/shrinkof the first portion 401 and second portion 402, and folding of eachportion influenced by the connection section 403, so that thedeformation mode is more stable as compared with the buckling phenomena,which inherently has an unstable feature. Therefore it become possibleto suppress change in deformation mode caused by slight deviation ofdimension, installation condition and constraint condition which mayoccur during manufacturing and installation phases. Moreover, since theimpact absorber device 400 of the fourth embodiment of the presentinvention absorbs the impact energy by uniformly deforming the entirefirst portion 401, second portion 402, and connection portion 403, andtherefore energy absorption efficiency, that is the total amount ofabsorbed energy divided by unit weight of the impact absorber device, ishigher than that of the conventional impact absorber device. FIG. 20shows a table comparing the energy absorption efficiency of severalimpact absorber devices. The energy absorption efficiency of the fourthembodiment of the present invention achieves 57.7 KJ/kg, which is about4.4 times as compared with the conventional impact absorber device.Since the structure of the impact absorber device 400 is simple, designfeatures such as peak load and load-to-length-change relationship can beeasily estimated, and the impact absorber device 400 can be easilymanufactured with reduced cost. Moreover, since the impact absorberdevice of the present embodiment is integrally formed into one unit, theimpact absorber device may cover various load displacements and mayeasily control various energy absorptions. Furthermore, since the impactabsorber device 400 has no relative sliding portion between theexpanding element and shrinking element owing to the integrally formedstructure, which is necessary for the impact absorber device of thefirst embodiment, it becomes possible for the impact absorber device toprovide highly rigid property and resistance property against bending,shearing, vibration, and so forth, and also it becomes easier for theimpact absorber device to be installed at a necessary location. Further,in the impact absorber device 400 of the fourth embodiment, the innerdiameters of the first portion 401 and second portion 402 and connectionportion 403 are the same to each other, and therefore this device issuitable for manufacturing by casting, making it easy for manufacturing.Further, as described above, the inner diameter of the first portion 401hardly changes during the deformation. Therefore the unit 410 can besecurely fixed to a designated installation location by merely fixingboth ends thereof to the rigid plates, thereby making it possible forthe impact absorber device to achieve specified performance even thoughthe impact absorber device is subject to vibration, or the impactabsorber device receives the impact in a diagonal direction.

1. An impact absorber device, comprising at least one first portionhaving a short tubular shape, and at least one second portion having ashort tubular shape concentrically disposed in a stacked relationshipwith said first portion, wherein said first portion and said secondportion engage with each other at an engagement portion which isinclined with respect to a concentric axis of said first portion andsaid second portion, wherein the first portion has a small diameter andhas a full peripheral sliding contact face at a top portion thereof, thesecond portion has a large diameter and has a full peripheral slidingcontact face at a bottom portion thereof, the engagement portion is atruncated cone connecting the first portion and the second portion sothat the full peripheral sliding contact faces are directed in oppositedirections, the first portion, the second portion and the connectionportion constitute one unit, the impact absorber device furthercomprises support elements for supporting one or a plurality of theunit(s) from both sides, and the support element has a sliding contactsurface on a side facing the unit.
 2. The impact absorber deviceaccording to claim 1, wherein each of the first portion and the secondportion has a short cylindrical shape of which cross-section is acircle, a short tubular shape of which cross-section is an ellipse, or ashort tubular shape of which cross-section is a polygon.
 3. The impactabsorber device according to claim 1, wherein the impact absorber devicehas a plurality of the units, and adjacent units abut to each other atthe full peripheral sliding faces of the first portions.
 4. The impactabsorber device according to claim 1, wherein the impact absorber devicehas a plurality of the units, and adjacent units abut to each other atthe full peripheral sliding faces of the second portions.
 5. The impactabsorber device according to claim 1, wherein the impact absorber devicefurther comprises a sliding element which has sliding faces on bothsides, the impact absorber device has a plurality of the units, andadjacent units are disposed in such a manner that the full peripheralsliding contact face of the first portion and the full peripheralsliding contact face of the second portion face each other via thesliding element.
 6. The impact absorber device according to claim 3,wherein the units are different from each other in shape or in material.7. The impact absorber device according to claim 1, wherein each of thefirst portion and the second portion has a short cylindrical shape, andradiuses of the cylindrical shapes of the first portion and the secondportion respectively measured on the basis of the center of wallthickness thereof are different from each other.
 8. The impact absorberdevice according to claim 7, wherein the impact absorber device has oneor more units, each of which further comprises two of the first portionsand one of the second portion disposed therebetween.
 9. The impactabsorber device according to claim 7, wherein the units are differentfrom each other in shape or in material.